Conventional laser fault isolation techniques for circuit analysis such as laser voltage probing (LVP) and dynamic laser stimulation (DLS) use an infrared laser as silicon is relatively transparent to infrared wavelengths. Although infrared laser light may thus penetrate through the substrate to illuminate the active circuits, the spatial resolution for conventional laser fault techniques is limited by the relatively long wavelengths of infrared light. The spatial resolution for conventional techniques has thus become too coarse for advanced process nodes such as 14 nm or smaller.
To provide sufficient resolution for advanced process nodes, various laser fault isolation techniques have been proposed that utilize visible lasers due to the relatively short wavelengths for visible light as compared to infrared illumination. An example visible laser fault analysis system 100 is shown in FIG. 1. A thinned die 115 is mounted in a carrier 120 that is in turn held by a socket 130. The active surface of thinned die 115 faces carrier 120 so that electrical connections may be made to drive the circuitry within the active surface. The backside of thinned die 115 contacts a solid immersion lens (SIL) 110 held by a backing objective 105. Silicon is very absorptive to visible light such that the backside of thinned die 115 must be ground down until thinned die 115 is approximately 2 microns in thickness. The resulting silicon substrate for thinned die 115 is very fragile and readily cracked as SIL 110 must be in contact with thinned die 115 for proper imaging. In addition, the thinned silicon substrate has low thermal mass such that it is prone to overheating during the fault analysis. Conventional fault analysis with visible light is thus hampered by die fragility and overheating issues.
Accordingly, there is a need in the art for improved fault analysis tools and techniques using a visible laser light source.